The present invention relates to a double acting reciprocating hydraulic pump, comprising a pump body within which there is mounted a sector which oscillates about an axis and which acts as a piston. In the art this type of hydraulic pump is called a semi-rotary pump.
In known semi-rotary pumps the pump body is generally a fixed cylinder and having two distributor valves, the valve members of one valve being formed in the oscillating sector, and the valve members of the other valve being formed in the inlet duct of the pump. Operation of the oscillating sector is effected manually. Such pumps work satisfactorily only at low frequencies, for which reason their range of application is extremely limited; in practice these semi-rotary pumps have been utilised only for transferring liquid from one container to another.
When a consistent head, good operational reliability and high delivery rates are required it has previously been necessary to utilise rotary pumps of the axial piston type in which the pistons are arranged in a cylinder block which rotates about an axis coincident with the axis of the drive shaft of the pump (in-line pumps) or alternatively rotates about an axis inclined with respect to the drive axis of the pump (bent-axis pumps).
These rotary pumps have automatic valve gear for the auto-distribution of hydraulic fluid by one of the following techniques:
by means of appropriate openings in communication with one another and formed in the cylinder block, which openings are further in communication, respectively, with the outlet and the inlet of the pump and are uncovered by the movement of the pistons relative to the cylinder block;
by means of automatic valves provided on the output and by means of auto-distribution with openings provided in the inlet.
Such pumps have very complex structural and functional characteristics, require accurate manufacture of all their components, have to be made of appropriate materials, in particular suitable low-friction metal alloys, for example an alloy of silver, antimony and tin, particularly for the manufacture of the relatively movable parts. Such pumps also require accurate and frequent maintenance, and consequently these pumps are expensive to manufacture, to operate and to maintain.
The main object of the present invention is to provide a semi-rotary pump which is usable for medium and high heads, with a reliability and an efficiency least comparable with those of the known rotary pumps referred to above, but with structural and functional characteristics significantly simpler than the said known pumps.